1. Technical Field
The invention relates to a system and a method for securing the communication of components within self-service automats, in particular automated teller machines.
2. Discussion
Self-service automats often have a series of components that have to be linked to each other. Usually, these automats have a standardized PC platform that meets special security requirements. Keypads, cash dispensing automats, card readers, monitors and other devices are connected to this PC platform (motherboard), by USB interfaces for example.
These automats further include the possibility of connecting to another computer so that a maintenance engineer, for example, can connect to the self-service automat using his laptop.
A situation of this type exists, for example, when the engineer would like to test the money dispensing unit. Using a test program that is installed on the laptop, he can connect to the dispensing unit in order to dispense bills for test purposes. In addition, instances are known in which persons use this technology in order to procure cash in an unauthorized fashion. This latter is achieved by circumventing or manipulating physical security mechanisms.
Furthermore, security-sensitive cases are known in which a person using a USB tracer (a device that listens in on the traffic on the USB interface) switches to the line of the dispensing unit and the PC for the purpose of analyzing control commands, manipulating them and re-entering commands overheard in order to obtain cash in an unauthorized manner in this way. Furthermore, cases are known in which a person using a USB tracer interposes himself between the line for the card reader and the PC in order to obtain card data in an unauthorized manner.
The present invention is not categorically restricted to USB; however, USB is a dominant standard for peripheral devices on computers so that in what follows the discussion will center essentially on USB. However, it should be noted that all other connecting standards that may similarly be wireless and follow a similar concept to USB, are to be covered by the invention.
USB is a serial-bit bus, the individual bits of the data package are transmitted sequentially. Data transmission takes place symmetrically over two twisted wires, one of which transmits the data signal unchanged, the other the inverted signal. The signal receiver creates the voltage differential between the two signals; the voltage swing between levels 1 and 0 is consequently twice as great, irradiated interference is largely eliminated. This increases transmission security, suppresses interference and improves electromagnetic compatibility. Two additional wires are used for the power feed to the attached devices. By using only four strands in one cable, said strands can be made thinner and more economically than with parallel interfaces. A high data transmission rate can be achieved at relatively low cost since it is not necessary to transmit several signals with identical electrical and chronological profiles.
The bus specification provides for a central host controller (master) that assumes coordination of the connected peripheral devices (the slave clients). Theoretically, up to 127 different devices can be connected to the host controller. Only one USB device can be connected to a USB port at a time. If several devices are to be connected to a host, a distributor (hub) must handle the connection. The result of using hubs is the creation of tree structures that all end in the host controller.
In spite of its name—Universal Serial Bus—the USB is not a physical data bus. In a bus of this kind, several devices are connected in parallel to one line. The designation “bus” refers to the logical networking, the actual electrical implementation is carried out using only point-to-point connections.
A USB stack on which the appropriate USB drivers for the devices sit is used to manage information and data transmitted over the USB bus. The USB stack is responsible for the assignment of information to the individual device drivers.
FIG. 1 shows a stack structure of this kind for two devices. The left column represents the stack structure for a system PC that basically controls the automated teller machine. The RM3 device is a peripheral device that is connected to the system PC over a USB bus for example. This peripheral device may be, for example, an automated teller machine or a card reader in which in turn an operating system is similarly located that manages the USB interface. It can be seen that the system PC has a JDD (Java device driver) layer that is responsible for loading the drivers. Below said JDD is located an object request broker (ORB). The USB transport layer, which in turn sits on the USB driver, is located below said ORB.
It must be noted that the USB technology has no form of security functions so that the manipulations described above can occur.